One of the hidden Mickey’s at Mulholland Madness is located on a billboard near the entrance queue.  Look out for a swimming pool in the shape of a hidden mickey.  It’s right next above a sign that says "Alamo Rent A Car" and below a house with a tennis court.

Here is a picture of the Mulholland Madness Pool Hidden Mickey.

There are a few hidden Mickeys at the Mulholland Madness roller coaster at Disney’s California Adventure. 

if you look on the billboards at the entrance of the ride you will find a California license plate that says "ADVNTUR".  If you look closely at the tab on the license you will see a small black classic hidden Mickey.

Below is a picture of the license plate hidden Mickey on the billboard near the entrance queue at Mulholland Madness.